1. Field of the Invention
The present invention relates to a cutting tool assembly and, more particularly, relates to a novel holding device for cutting tools, especially such as flat beaded drill bits which are employed in the drilling of track rail.
Over the course of many years, track rail has generally been drilled on site during track-laying operations, in order to enable adjoining sections or lengths of track rail to be bolted together through apertured connecting plates and bolts. Basically, the holes are drilled in the track rails through the intermediary of a hole drilling apparatus which is clamped to the track rail during the drilling operation, and which is well known in this technology as a rail drill, wherein the whole cutting tool, which is constituted of a flat beaded track drill bit, is clamped in a cutting tool holder known as a "Rich Chuck".
2. Discussion of the Prior Art
This particular cutting tool holder is of the general configuration of a solid, cylindrical member which is longitudinally split into two mating halves, each being substantially semi-circular in cross-section. The facing surfaces of the split cylindrical holder are each provided with a central, longitudinally extending groove or recess which, when the track drill bit is inserted therebetween, causes opposite faces on the track drill bit to contact the facing surfaces on the holder, and longitudinal beads provided on the opposite faces of the track drill bit to engage in the respective grooves or recesses in the facing surfaces tool holder halves. Thereafter, the entire cutting tool assembly, constituted of the cutting tool holder and the inserted track drill bit, is hammered into a spindle on the rail drill so as to cause the holder to clampingly engage the track drill bit. The track drill bit, upon insertion into the tool holder, has the cutting end thereof extending for approximately three to six inches, with the projecting end of the track drill bit having cutting surfaces formed thereon for effectuating the drilling of holes through the web of the track rail. The drilling of accurately sized and located holes in track rail with this type of cutting tool assembly employed in current rail drills is subject to a number of drawbacks and disadvantages.
Thus, the considerable unsupported length of tool drill bit projecting axially from the cutting tool holder presently causes the leading cutting end of the drill bit to assume an excessive extent of runout or eccentricity during drilling, inasmuch as even any minor misalignment of the clamped portion of the drill bit between the mating halves of the tool holder due to manufacturing tolerances or caused by the hammering of the holder into the rail drill will result in an extensive runout, possibly up to as much as 0.060 tir, of the drill cutting surfaces.
Moreover, inasmuch as the steel employed for track rail has been considerably improved upon in recent years; for instance, through the provision of harder steels, whereby such track rail is now designated as "Head Hardened Rail", this has dramatically increased the wear on the cutting surfaces of the tool drill bits, necessitating their frequent replacement after the drilling of only relatively few holes in the track rail.
In order to replace such worn tool bits, it is the current practice in rail drills employing the above-mentioned "Rich Chuck" or such similar cutting tool assembly, to hammer the assembly constituted of the tool holder and the drill bit as a unit out of the rail drill, separate the halves of the holder, remove the worn drill bit, insert a new drill bit between the mating halves of the tool holder, and then hammer the entire cutting tool assembly back as a unit into the rail drill. This sequence of installing and replacing the drill bits is extremely time-consuming, while in addition thereto, the need for hammering the entire assembly into and out of the rail drill, not only results in misalignments of the drill, thus causing excessive runout and wear, but may also impart damage to the tool holder and drill bit so as to render these parts unuseable.
Consequently, in order to improve upon currently employed cutting tools for the drilling of, in particular, track rail, the present invention contemplates the provision of an improved cutting tool assembly incorporating a novel flat beaded track drill bit, and a novel holder for the drill bit which will eliminate the necessity for having to remove the tool holder from the rail drill and to then reinsert the holder during each replacement or interchange of drill bits. Moreover, the inventive drill bit can be easily inserted and clamped in the holder, and thereafter withdrawn therefrom through the simple manipulation of a clamping element arranged in the tool holder. There is also effectuated an extensive reduction in the length of the drill bit, resulting in a savings to material, considerably reducing any runout of the cutting end which will ameliorate deleterious effects due to runout or eccentricity which generally causes one of the cutting edges of the drill to assume most of the cutting action, thereby imposing unnecessary strains and stresses on the drill bit and on the tool holder, and consequently considerably enhancing the life expectancy of the components of the cutting tool assembly.
Moreover, eliminating the necessity for the removal and reinsertion of the tool holder in the rail drill during replacements of the drill bit, considerably reduces the "downtime" or servicing time for the rail drill during this sequence of operation.
The advantages obtained by the inventive cutting tool construction for rail drills impart a reduction in the overall length of the drill bit of up to 50% in comparison with present drill bits employed with the "Rich Chuck" for rail drills, while considerably increasing the rigidity and strength of the cutting tool assembly during its drilling operation.
Furthermore, a tightened radius geometry in the bead construction of the inventive track drill bit enables the latter, in combination with being mounted on the inventive tool holder, to run more concentrically within 0.012 max tir, in contrast with a runout in the current state-of-the-art of up to 0.060 max tir, thereby increasing the accuracy of the drilled holes in the track rail.
Although numerous and widely varying types of arrangements and holders are currently known in the technology relating to the mounting of cutting tools, such as drills and the like, these are generally more complex in construction and function, frequently impose undue levels of stresses on the clamped or restrained portions of the cutting tools; and are not particularly suited for use with rail drills.
Williams U.S. Pat. No. 2,621,548 discloses a mounting for cutting tools, in which a generally cylindrical tool holder includes a slotted shank portion extending from a rotary drive mechanism. The slotted shank portion of the tool holder is adapted to receive a spade drill bit having a base portion with a slot formed therein, which extends over a fastening screw extending across the slot in the shank of the tool holder. In this instance, the screw generally extends through an opening formed in the spade drill bit, and upon being tightened to clamp the drill bit in the tool holder, imparts stresses to the drill bit during drilling operation, while also necessitating the complete removal of the screw in order to remove or exchange the spade drill bit.
Pollington U.S. Pat. No. 4,488,840 discloses a rotary cutting tool in which a cutting insert is secured in a slotted portion provided on a cylindrical tool holder, and thereafter soldered thereto in order to securely attach the insert to the holder. This necessitates the insertion and removal of the entire cutting tool assembly constituted of the tool and the holder into a drilling machine, and fails to facilitate for the simple replacement of drill bits in a tool holder as contemplated by the present invention.
Benjamin U.S. Pat. No. 3,776,656 discloses a spade drill bit which is adapted to be inserted into the slot formed in a cylindrical shank portion of a tool holder. A screw extends through the slot and through a hole which is formed in the drill bit, and upon being tightened causes the surfaces of the slot to clampingly engage the spade drill bit. This particular structure fails to provide the necessary precision in inserting a drill bit into the holder and, moreover, necessitates the complete removal of the clamping screw in order to be able to, respectively, insert and remove the drill bit from the tool holder.
Field U.S. Pat. No. 4,334,446 discloses a cutting tool holder having a slotted end for insertion of a triangular cutting tool, including a clamping member in the form of a screw extending across the slot, in which the screw may be tightened or loosened to selectively clamp or release the triangular cutting tool which is inserted in the holder slot towards one side of the clamping screw. This particular structure fails to provide for the precise alignment of a flat beaded track drill in a tool holder slot of the type under consideration herein, and is not readily adaptable for use in rail drills.